Switch for a suspension railroad

ABSTRACT

An improved switch for use in a syspension railroad system utilizing the electrodynamic suspension principle in which a separate normal flux system is provided having roadway members located outboard of a suspension system for the main roadway extending from the plane of the main roadway to the plane of a branch roadway vertically displaced from the main roadway, which members cooperate with extendable and retractable members in the vehicle whereby with said vehicle members retracted travel along the main roadway results and with said vehicle members extended travel to the branch roadway results.

Miericke 1 1 July 29, 1975 [54] SWITCH FOR A SUSPENSION RAILROAD3,763,788 10/1973 Pougue 104/130 3,777,667 12/1973 Perrott 104/130 [75]Inventor: Jurgen Mlerlcke, Nurnberg.

Germany Primary ExaminerM. Henson Wood, Jr. Assigneer SiemensAktiengesellschaft, Munich, Assistant E.raminerRichard A. Bertsch rm nyAttorney, Agent, or Firm-Kenyon & Kenyon Reilly 22 Filed: May 1, 1974 1N 46 ,751 r [2 1 App] 5 57 ABSTRACT [30] Foreign Application PriorityData An Q FF Switch for use In syspenslqn railioafi system utilizmg theelectrodynamic suspension pr1nc1- May 5, 1973 Germany 2322150 p in whicha Separate normal flux System is provided having roadway members locatedoutboard of a sus [52] U.S. Cl. 104/130; 104/148 MS pension System forthe main roadway extending from hilt. the plane of the main y to theplane of a [58] Fleld 0f Search 104/130, 148 MS, 148 SS, branch roadwayt ly displaced from the main 04/148 LM roadway, which members cooperatewith extendable and retractable members in the vehic1e whereby with 156]References cued said vehicle members retracted travel along the mainUNITED TATE P T T roadway resu1ts and with said vehicle members ex-3,680,488 8/1972 Donlon 104/130 tended travel to the branch roadwayresu1ts. 3,712,238 1/1973 Colovas et al...... 3,738,281 6/1973 Waidelich104/148 MS 13 Clam, 3 Drawmg 8" SWITCH FOR A SUSPENSION RAILROADBACKGROUND OF THE INVENTION This invention relates to magneticsuspension railroads in general and more particularly to an improvedswitching arrangement for use in such railroads.

Various systems have been developed for use in electrodynamicallyguiding a suspended vehicle. Such suspension systems are operable withvehicle velocities of approximately 300 km/hour and more. Generally, inall of these systems, as the vehicle moves along the track, currents areinduced in electrically conducting support and/or guidance elementsarranged along the roadbed by superconducting magnetic coils attached tothe vehicles. These elements on the roadbed comprise, for example,electrically conducting plates or conductor loops extending in thedirection of travel of the roadbed, and are also referred to as reactionmembers. The currents induced therein exert repelling forces on themagnetic coils for supporting and/or guiding the vehicle along thetrack.

The simplest system of this nature is called a normal flux system andcomprises a horizontally disposed conducting plate running along theroadbed over which the magnet coil moves with the magnet coil alsodisposed in a horizontal plane. As the magnet coil appraoches the plate,the repulsion forces become larger causing the separation between theplate and magnet coil to increase and thus hold the magnet coilsuspended. In addition to the lifting forces, which oppose the force ofgravity of the vehicle, braking forces are also induced due to the ohmicresistance of the conducting plate, which forces have a directionopposite to the travel direction of the vehicle.

In a paper published in the Journal of Applied Physics, vol. 43, (1972),pp. 2680-2691 by Richards et al. a system in which braking forces andlosses are relatively small has been described. This system is called azero flux system and includes superconducting magnet coils mounted onthe vehicle and arranged in pairs arranged one above the othervertically. The two coils are excited in mutually opposite directionsand are guided above and below an electrically conducting plate which iscoupled to the roadbed and disposed generally horizontally. With such anarrangement, particularly if the plate is thin relative to the depth ofpenetration of the magnetic field into the plate material, low lossesresult. With the exception of small losses produced in the centerportion which causes braking forces, only if the plate is not situatedin the center between the coils of the respective coil pairs are anysignificant losses produced. The braking force produced is in the firstapproximation proportional to the square of the excursion of the centerposition while the lifting force produced is in the first approximationdirectly proportional to the excursion. As compared to other systems inorder to obtain lifting forces for a vehicle of the same weight, twomagnet coils are required as compared to one magnet coil in the normalflux system mentioned above. A similar zero flux system in which thesupport rail mounted on the roadbed is not a conducting plate but is amultiplicity of conductor loops arranged one next to the other in thedirection of travel has been described in an article by Powell et al.published in the Journal Cyrogenics and Industrial Gases vol. 4, pp.19-24, (1969).

Clearly, the cost of the installed rail line for use in suspendedrailroads of this nature is quite expensive. As a result, it isconsidered to be more economical to run a single track over longdistances with appropriate branch tracks provided to permit vehiclestraveling in opposite directions to pass each other. This requires theswitches to be provided to guide vehicles onto these branch tracks orsidings to allow such passage. As a result, various types of switchingsystems have been developed. One such system requires that the vehiclebe severely braked ahead of the switch to the point where it is nolonger in suspended guidance. Vehicles of this nature are typicallyequipped with auxiliary wheels which can ride on conventional tracksduring starting and stopping and in case of emergency. Thus, in thissystem, the vehicle is slowed down to the point where it runs inconventional fashion with wheels on tracks and is guided off the maintrack and onto a siding using a conventional railroad switch.

Another type of switch has been disclosed in U.S. Pat. Application Ser.No. 399,940 now Pat. No. 3,841,227. In general terms, this systemcomprises two U-shaped guidance channels of non-magnetic electricallyconducting material which are attached to and run along the roadbed eachcomprising an upper and lower part disposed in planes essentiallyparallel to the roadbed, i.e., horizontal and a lateral part disposedapproximately perpendicular thereto. Pairs of superconducting magnetsare mounted on the vehicle, with at least two pairs on each sidethereof, and are arranged so that one magnet of each pair is situatedbetween the upper and lower parts of the U-shaped channels and that thesecond of the pair is vertically above the upper part of the channel.Thus, the lower coil in conjunction with the lower part forms a normalflux. In the area of the switch, only the lower part of the guidancechannel is provided along with a movable lateral part. Thus, in the areaof the switch only a normal flux system is provided to supply thenecessary lateral forces. The displaceable lateral parts provide goodhorizontal guidance through the region of the switch. If a linear motorpropulsion motor is used for propelling the vehicle, the armature railsof the linear motor are positioned along the roadway or shiftedhorizontally with respect to the roadway within the switch oralternatively propulsion in the switch area can be dispensed with andthe switch traversed by inertia. In addition, the parts which areshifted horizontally need not consist of one piece but can be assembledin a sectional manner which section when setting the switch can then beshifted laterally to different degrees. In another embodiment, in orderto set the switch the movable parts are moved down for straight aheadtravel and other side parts moved up for branching off from onto theswitch track.

In addition to these systems and others which permit branching off inthe horizontal plane onto a track lying in the same plane, a switchingsystem in which the vehicle is switched to a branch track in a separatevertical plane has also been disclosed. Such an arrangement is shown inthe paper entitled The Magnet Plane Guided Electromagnetic Flight ModelPaper," (Massachusetts Institute of Technology, Cambridge, May 1, 1972,p. l-lO). In the disclosed arrangement, a vehicle equipped withsuperconducting coils is guided by electrodynamic suspension in a troughshaped aluminium track. A roadway section about a mile long is mountedon sliding bearing blocks which permits the connection of the roadwaywith a parallel roadway which is in a horizontal plane above the normalroadway. When operating at higher speeds such as above I km/hour, largeradii are required for switches of this nature and thus, mechanicallymovable sections of relatively long length must be provided. As aresult, the apparatus for moving these long sections of track within theswitch becomes extremely expensive.

In view of the deficiencies of the prior art switches, it is the objectof the present invention to provide an improved switching arrangement ofthis general nature, which arrangement fulfills all requirements withoutbeing excessively costly.

SUMMARY OF THE INVENTION The present invention solves this problem byinstalling in the vehicle mechanically movable means which are capableof reacting with additional fixed means mounted on the roadbed in thearea of the switch to thereby provide an additional guidance arrangementoperative only within the switched area. In a first illustratedembodiment, the means mounted in a mchanically movable manner on thevehicle comprise an additonal set of superconducting coils and the meansmounted on the roadbed additional conducting plates (reaction rails) tocooperate therewith to form a normal flux system. The reation railswithin the switch which form part of this separate suspension system areinclined so that they can guide the vehicle upward to a branch trackwhich is vertically above the main track in a separate horizontal plane.This switch permits contactless change fron one roadway to the otherwhile utilizing the electrodynamic principle and is capable ofsupporting vehicles operating at high speeds. Furthermore, the switchhas no moving parts. The parts in the vehicle which must be moved in theswitched area are relatively small. As a result, the switch can have alarge radius of curvature at the point where it branches off and thuscan be traversed at high speeds. As a result, continuous transfer to thebranch track is assured without endangering safe guidance of thevehicle.

According to a further embodiment of the invention, the auxiliaryguidance system comprises magnets installed on the roadbed whichcooperate with retractable reaction rails on the vehicle. Thisarrangement offers further advantages with regard to propulsion of thevehicle within the switch region.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional viewthrough a portion of a switch according to the present invention alsoillustrating the lower portion of a vehicle with respect to the switch.

FIG. 2 is a perspective view of a portion of the roadbed of FIG. 1.

FIG. 3 is a cross sectional view through an alternate embodiment of aswitch according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a crosssectional view looking in the direction of travel of a switch accordingto the present invention. The main track right-of-way rests on a roadbed2 with the branch track located vertically above and resting on aroadbed structure 2a supported in suitable fashion. The point at whichthe cross section of FIG. 1 is taken is at a point illustrated on FIG.2. That is, it is at the point of entrance into the switch. Shownassociated with the lower main track section is a vehicle 1 which isassumed to be in a suspended state with respect to the roadbed.Similarly, a vehicle la is shown on the branch track located verticallyabove the main portion of the track. At the entrance to the switch, tworeaction rail arrangements designated 3 and 4, one on each side of theroadbed 2 are provided. The reaction rail arrangement 3 is made up of ahorizonal rail 5, a vertical rail 6, another horizontal rail 7 andanother vertical rail 8. Similarly, the arrangement 4 is made up ofhorizontal rails 9 and 11 and the vertical rails 10 and 12. As can beseen more clearly by viewing FIGS. 1 and 2 together, the reaction rails5 and 6 and 9 and 10 remain in the plane of the roadbed 2 continuing onas the main portion of track. The rails 11 and 12 and 7 and 8 however,are sloped upwardly to the branch track located above the roadbed 2,i.e., to the branch track on the roadbed 2a. The reaction rails 9 and 10and 5 and 6 are used for straight ahead travel on the main track and thereaction rails 7 and 8 and 11 and 12 for travel onto the branch tracksupported thereabove on the roadbed 2a. Suspension of the vehicle whenon the main portion of track is obtained through the intereaction ofsuperconducting coils 13 and 14 located on opposite sides of thevehicle, with their respective reaction rails 9 and 10 and 5 and 6 toform a normal flux system. Shown are coils l5 and 16 located directlyabove the coils 13 and 14 with a gap in between. These groups of coilscan be used to form a zero flux system on straight portions of the trackoutside the switch at which point a reaction rail will be locatedtherebetween. A zero flux system of this nature is disclosed in theabove reference article in the Journal of Applied Physics. The coils 15and 16 are mounted on the body so as to be movable in a horizontaldirection to the position shown by dotted lines. If it is desired totravel straight through the track, these coils remain in their inwardposition shown in solid lines and support of the vehicle results fromthe normal flux system obtained from the interaction between the coils13 and 14 and their associated reaction rails 5 and 6 and 9 and 10.However, if it is desired to switch to the upper branch track supportedon the roadbed 2a, the coils l5 and 16 are extended to the positionshown in dotted lines. In that case, the coils l5 and 16 which, like thecoils 13 and 14, are also preferably superconducting magnet coils willform with the respective reaction rail 7 and 8 and 11 and 12 a separatenormal flux system. Since the rails 7 and 8 and 11 and 12 are slopedupwardly, to the vertical branch track above the main track, the vehiclewill be guided in that manner until it reaches the required level. Theslope or radius of curvature of these rails is selected in accordancewith the necessary requirements as to speed and so on. It will berecognized that in order to maintain high speed operation, the slopemust be very gradual and thus will extend over a considerable distance.

Propulsion of the vehicle may be obtained through the use of a linearmotor designated generally as 20, having active windings 21 and 22mounted within the vehicle. In the embodiment illustrated on FIG. 1,these windings 21 and 22 are shown dashed since they are partiallyhidden by the magnet coils 26 and 27. The windings 21 and 22 areseparated by a predetermined air gap 23. Protruding into the air gap 23is a reaction rail 24 extending vertically from the roadbed 2. Thereaction rail 24 is approximately centrally located between the reactionrail arrangements 3 and 4. This rail which can be made of aluminum forexample, provides the armature of the linear motor 20. As illustrated,between each winding 21 and 22 a gap of dimension 25 will exist.

The coils 26 and 27 serve to maintain lateral guidance of the vehicle.Again, these will preferably be superconducting magnet coils and asshown are mounted on each side of the rail 24. The rail 24 thus acts asan armature for the linear motor and at the same time can act as thereaction rail cooperating with the coils 26 and 27 to maintain lateralguidance. In addition, the lateral guidance system can be controlled soas to properly maintain the gaps 25 between the excitation windings 22and 21 of the linear motor 20 and the reaction rail 24. In addition tothe lateral guidance forces obtained from the coils 26 and 27 along withreaction rail 24, additional lateral guidance is obtained from theinteraction of the superconducting coils 13 and 14 with the verticalreaction rails 6 and 10. Similarly, for switched operation, thesuperconducting coils l5 and 16 interact with the vertical rails 8 and12 to aid in lateral guidance.

From viewing FIGS. 1 and 2, it is apparent that during a switchedoperation where the vehicle is being moved to the branch track of theupper roadway 2a, the rail 24 will gradually come out of the gap 23beween the windings 21 and 22 and thus, the linear motor will steadilybecome less effective until at some point it has no effect at all.Considering this type of operation, the necessity of obtaining lateralguidance from the reaction rails 8 and 12 also becomes evident. Theresult of the loss of the cooperation between the rail 24 and coils 21and 22, is that the vehicle steadily loses speed within the switchedarea. That is, there is a gradual loss of propulsion power and at thesame time an increase of braking forces. As' a result, the vehicle mustenter the switch at a high enough speed so that it can reach the upperroadway 2a on which a reaction rail 24a is provided at which pointpropulsion will be resumed.

A further embodiment of the present invention is shown on FIG. 3. Inthis embodiment, a vehicle 30 is suspended above a roadbed 2. Only thelower roadway is shown with the portions of the system extending to theupper road broken off. These would, of course, be extended to an upperroadway in the manner shown on FIG. 1. The vehicle again is providedwith sets of coils 37 and 38 and 39 and 40 on each side which duringnormal operation can be used with an appropriate rail to form a zeroflux system. For straight through travel in the switch area, the coils37 and 39 cooperate with reaction rails arrangements 31 and 32 in themanner described above in connection with FIG. 2. That is, the coil 37cooperates with the horizontal reaction rail 33 and the verticalreaction rail 35 and the coil 39 with the horizontal reaction rail 34and the vertical reaction rail 36. As in the previously describedembodiment, the coils 37 through 40 will preferably be superconductingmagnet coils. However, in this embodiment, rather than mounting theupper coils 38 and 40 for horizontal motion when switching is desired,horizontally extendable and retractable reaction rails 43 and 44 areprovided in the vehicle. Normally, they will be in the retractedposition shown with the rail in dotted lines.

When extended, they will be in as in the cross sectional illustrationwith the portion of vehicle body supporting them being in the positionshown in dotted lines. Along the roadbed on each side are provided alarge number of controllable electromagnets designated 41 and 42. At theentrance to the switch, these lie in horizontal planes and will thenfollow a sloped path as indicated to the upper roadway. Theseelectromagnets cooperate with the extended reaction rails 43 and 44 toguide the vehicle to the upper roadway. The reaction rails 43 and 44which may be made of aluminum for example, will produce a lifting aswell as a lateral stabilization force. Furthermore, this arrangement canbe used for propulsion of the vehicle within the switched region. Such asuspension, guidance and propulsion system is described inElectrotechnische Zeitschrift edition B, vol. 23, No. l3, p. 3l l-3l3(I971). Thus, the problem of the previous embodiment which required highspeed entrance into the switch is eliminated in this embodiment.

If straight through travel is desired, the reaction rails 43 and 44 areretained in the retracted position and guidance of the vehicle throughthe switch is in the manner described above in connection with FIG. 1with propulsion provided by the linear propulsion motor 20. If it isdesired to branch to the upper roadway, the reaction rails 43 and 44 areextended and the magnet coils 41 and 42 energized. As noted above, theelectromagnets 41 and 42 are installed along the desired slope or radiusof curvature much in the manner described aboved in connection with thereaction rails of FIGS. 1 and 2. These magnets may be properly operatedto provide, as noted above, suspension, guidance and propulsion withinthe switched area, thus causing the vehicle to be transported from thelower roadbed shown to an upper roadbed such as that illustrated on FIG.1.

Although not shown on the figure, the vehicles 1 and 30 will typicallybe provided with conventional retractable wheels. These may be typicalrailroad wheels which can cooperate with conventional rails installed onthe track or may be designed to roll directly on the roadbed 2.

As noted above, outside the switch area it is preferable that thevehicle be suspended and guided by a zero flux system which exhibitssmaller losses than the normal flux system used within the switch.Because of this, a transition at the point where the switch is enteredis necessary. That is, the vehicle must be gradually switched over frombeing guided by a zero flux system to being guided by a normal fluxsystem as described above in connection with FIG. 1. Since the lossesfor a normal flux system can be up to ten times as large as the lossesfor a zero flux system, a large amount of adjustment is necessary andthe transition cannot be allowed to occur suddenly. In order to achievea gradual transitiomaluminum rails of the zero flux system having across section which decreases as the vehicle enters the normal fluxsystem and leaves the zero flux system, i.e., when entering the switch,and through aluminum rails of the normal system having a cross sectionwhich correspondingly increases when entering the switch.

Although in each case, the reaction members on the roadbed have beendisclosed as continuous conducting rails which, in accordance with theelectrodynamic propulsion system being used, are non-magnetic, it willbe recognized by those skilled in the art that these continuous railscan be placed by individual conductor loops used as reaction elements.When employing conductor loops, these loops are generally arranged intandem at predetermined distances and are shortcircuited. In addition,it will be recognized that combinations of short-circuited conductingloops and continuous rails may also be used. These and other embodimentsmay be made without departing from the spirit of the invention which isintended to be limited solely by the appended claims.

What is claimed is:

1. In a suspension railroad system wherein vehicles are suspended usingthe electrodynamic repulsion principle, an improved switch for switchinga vehicle from the main roadway lying in a first horizontal plane to abranch roadway lying in a horizontal plane vertically displaced from thefirst plane comprising:

a. a first electrodynamic suspension system including first meansmounted in the vehicle and second means mounted on the main roadwaycooperating with said first means;

b. a second electrodynamic suspension system comprising third meanslocated on the roadway outwardly of said first means, and third meansextending from said main roadway to the branch roadway in a differenthorizontal plane and fourth means in the vehicle for cooperatingtherewith, said fourth means being mechanically movable between aretractd position where they are clear of said third means on theroadway and an extended position where they are above said third meanson the roadway to cooperate therewith.

2. A switch according to claim 1 wherein said third means located on theroadway comprise reaction members located on each side of the roadwayand wherein said fourth means in the vehicle comprise at least twomagnet coils, one arranged on each side of the vehicle.

3. A switch according to claim 2 wherein said third means on the roadbedcomprise reaction rails which cooperate with said magnet coils to form anormal flux system.

4. A switch according to claim 3 wherein said vehicle is suspendedoutside said switch area by zero flux system and further including atransition arrangement between said zero flux system and the normal fluxsystem in said switch area.

5. A switch according to claim 4 wherein the reaction members of thezero. flux system have a decreasing cross section in the direction ofentry into the switch and an increasing cross section in the directionaway from the switch.

6. A switch according to claim 1 wherein said third means located on theroadway comprise magnet systems located on each side of said roadway andsaid fourth means in said vehicle comprise at least two reaction rails,one mounted on each side of said vehicle.

7. A switch according to claim 6 wherein said reaction rails are made ofnon-magnetic electrically conducting material.

8. A switch according to claim 6 wherein said fourth means on theroadway comprise electromagnets.

9. A switch according to claim 8 wherein the system made up of saidelectromagnets on said roadbed and said reaction rails on said vehicleforms an electrodynamic lift and propulsion system for the vehicle.

10. A switch according to claim 9 wherein said reaction rails andelectromagnets form a normal flux system.

11. A switch according to claim 10 wherein said vehicle is suspendedoutside said switch area by zero flux system and further including atransition arrangement between said zero flux system and the normal fluxsystem in said switch area.

12. A switch according to claim 11 wherein the reaction members of thezero flux system have a decreasing cross section in the direction ofentry into the switch and an increasing cross section in the directionaway from the switch.

13. A switch according to claim 1 wherein the radius of curvature ofsaid third means extending from said main to said branch roadway is afunction of the desired maximum speed at which a vehicle will traversethe switch.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 1 3 896 737 DATED Ju y 29, 1975 INVENTOMS) 3 Jiirgen MierickeIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the Foreign Applicatoin Priority Data change date to May 2, 1973-- incolumn 1 line 26, change "appraoches" to approaches-- in column 3, line22, change "mchanically" to mechanically-- line 27, change "reation" to-reaction in column 4, line 25, change "intereaction" to -interaction incolumn 6, line 31 change "aboved" to above in column 7, line 24,(claim 1) change "and third means" to said third means-- line 29, change"retractd" to --retracted Signed and Scaled this thirtieth Day ofDeamber 1975 [SEAL] Arlen.

RUTH C. MASON C. IAISIIALL DANN Arresting Officer Commissioner of hmmand Trademarks

1. In a suspension railroad system wherein vehicles are suspended usingthe electrodynamic repulsion principle, an improved switch for switchinga vehicle from the main roadway lying in a first horizontal plane to abranch roadway lying in a horizontal plane vertically displaced from thefirst plane comprising: a. a first electrodynamic suspension systemincluding first means mounted in the vehicle and second means mounted onthe main roadway cooperating with said first means; b. a secondelectrodynamic suspension system comprising third means located on theroadway outwardly of said first means, and third means extending fromsaid main roadway to the branch roadway in a different horizontal planeand fourth means in the vehicle for cooperating therewith, said fourthmeans being mechanically movable between a retractd position where theyare clear of said third means on the roadway and an extended positionwhere they are above said third means on the roadway to cooperatetherewith.
 2. A switch according to claim 1 wherein said third meanslocated on the roadway comprise reaction members located on each side ofthe roadway and wherein said fourth means in the vehicle comprise atleast two magnet coils, one arranged on each side of the vehicle.
 3. Aswitch according to claim 2 wherein said third means on the roadbedcomprise reaction rails which cooperate with said magnet coils to form anormal flux system.
 4. A switch according to claim 3 wherein saidvehicle is suspended outside said switch area by zero flux system andfurther including a transition arrangement between said zero flux systemand the normal flux system in said switch area.
 5. A switch according toclaim 4 wherein the reaction members of the zero flux system have adecreasing cross section in the direction of entry into the switch andan increasing cross section in the direction away from the switch.
 6. Aswitch according to claim 1 wherein said third means located on theroadway comprise magnet systems located on each side of said roadway andsaid fourth means in said vehicle comprise at least two reaction rails,one mounted on each side of said vehicle.
 7. A switch according to claim6 wherein said reaction rails are made of non-magnetic electricallyconducting material.
 8. A switch according to claim 6 wherein saidfourth means on the roadway comprise electromagnets.
 9. A switchaccording to claim 8 wherein the system made up of said electromagnetson said roadbed and said reaction rails on said vehicle forms anelectrodynamic lift and propulsion system for the vehicle.
 10. A switchaccording to claim 9 wherein said reaction rails and electromagnets forma normal flux system.
 11. A switch according to claim 10 wherein saidvehicle is suspended outside said switch area by zero flux system andfurther including a transition arrangement between said zero flux systemand the normal flux system in said switch area.
 12. A switch accordingto claim 11 wherein the reaction members of the zero flux system have adecreasing cross section in the direction of entry into the switch andan increasing cross section in the direction away from the switch.
 13. Aswitch according to claim 1 wherein the radius of curvature of saidthird means extending from said main to said branch roadway is afunction of the desired maximum speed at which a vehicle will traversethe switch.